1. Field of the Invention
The present invention relates to cross-linked, electrically conductive ion-exchange polymers, especially ion-selective homogeneous membranes, containing a reinforcing material of non-woven carbonized polyacrylonitrile (PAN) fibers, to a method of preparing the carbonized PAN reinforced (backed) membranes and to electrochemical cells employing the same. More particularly the invention is directed to ion-selective membranes of low resistivity having a reinforcing fabric of non-woven material derived from carbonized polyacrylonitrile and their use in electrodialysis (ED) for desalting liquids.
2. Description of the Prior Art
Many uses have been found for permselective membranes, one of which is the demineralization of water and another which is to process whey to remove salts therefrom. Apparatus employing ion-exchange membranes and their method of operation are well known in the art and are more fully described in U.S. Pat. Nos. 2,708,653, 2,848,403, 2,826,544, 2,863,813, 3,003,940, 3,239,442, 3,341,441, 4,115,225 and many others.
Ion-exchange resins have a solid phase consisting of a homogeneous polymer with covalently bonded dissociable ion-exchange groups and mobile replaceable counter ions associated with them. These resins can be formed into dimensional structures such as sheets or membranes. To increase the mechanical strength of the membrane and to allow their manufacture in reasonably large sizes a reinforcing structure or material is imbedded therein such as a synthetic fabric of, for example, a woven glass sheet or a woven modacrylic fabric. The prior art has employed a wide range of materials in the manufacture of the reinforcing fabrics. Such materials have included polyesters (Dacron.RTM.), polyamides (Nylon.RTM.), acrylics (Orlon.RTM.), modacrylics (Dynel.RTM. or Kanecaron.RTM.), vinylidene chlorides (Saran.RTM.), tetrafluoroethylene (Teflon.RTM.), glass (Fiberglas.RTM.) rayons, polypropylene and the like usually having a visibly open structure as found in woven type fabrics.